The present invention relates to a pneumatic vibrator, also known in the industry as pneumatic hammer, for de-coring of castings made from aluminium, steel and iron alloys.
For the purposes of the present description, the term de-coring refers, in general, to removal of sand material from foundry castings.
Also, for the purposes of the present description, the term castings refers to parts/objects obtained by casting metals into suitable moulds.
Patent WO2007006936 describes a pneumatic hammer or de-coring vibrator.
The vibrator or hammer comprises a jacket comprising holes for inlet and outlet of compressed air. Inside the jacket there is a mechanical assembly consisting of a cylinder in which a piston slides under the action of compressed air. Said piston comes into contact with a punch, which in turn hits the casting to be subjected to de-coring.
Said hammer comprises a connection flange that allows it to be anchored, through fasteners such as socket-head screws, to a de-coring machine.
Said jacket of prior-art hammers is made of cast iron to ensure the desired strength characteristics.
No hammers are known wherein the jacket is made of a material other than cast iron, particularly in the field of high-performance de-coring hammers.
Said jacket is made as one cast monolithic piece.
The use of cast iron significantly increases the total weight of the hammer and requires much milling work, and hence much labour, for making the hollow hole that houses the mechanical assembly.
The use of cast iron also poses some limits as concerns stress resistance, due to the rigidity of the material and the resulting difficult damping of vibrations, which can propagate to the de-coring machine with which the hammer or vibrator is associated.
It is also known that these hammers are to be used in adverse environments where temperatures are very high. In such working conditions, operators must carry out their tasks quickly. It is therefore necessary that de-coring hammers can be easily connected to and removed from the de-coring machine, like the one described in patent EP1995002A2.
The solutions according to the prior art turn out to be difficult to handle, because the various compressed air inlet and outlet circuits are arranged in different areas, thus requiring more work to connect and disconnect the various air circuits.
Also, the hammers must operate at high temperatures, and there is a risk that the mechanisms that generate piston motion upon intake of compressed air might expand, leading to increased friction between the parts, resulting in decreased efficiency of the hammer, and requiring periodic maintenance.
De-coring hammers require high performance in terms of exerted force and piston oscillation frequency, in order to ensure fast and accurate de-coring of metal or alloy castings.
The hammer's performance is mainly checked by constantly monitoring the pulse frequency of the air exiting the cylinder. This type of check is cheap, but suffers from much uncertainty.
Other checking methods also exist, which can monitor the oscillation frequency of the beating mass within the cylinder. This is done by means of a sensor located on the jacket surface. Normally said sensor is connected to a processing circuit external to the hammer.
Said sensor is not protected, and therefore, when removing a hammer, said sensor may suffer damage caused, for example, by shocks.
No hammer currently exist in the art which comprises an integrated sensor that is protected against shocks; as a matter of fact, since the jacket is made as one monolithic piece and has a shape dictated by the standards enforced by the manufacturers of the machines whereto such hammers will have to applied, no protections exist for such sensors.